This invention relates in general to ion projection print heads, and more particularly to an ion projection print head having a plurality of electrodes for modulating and assisting ion flow through a longitudinal slot.
Printing apparatus are generally categorized as impact or non-impact printers. Impact printers typically have an inking device, a paper transport, and a mechanism for mechanically impacting desired characters on transported paper through the inking device. Non-impact printers produce characters on transported paper electrically or optically rather than mechanically. The non-impact electrostatic printing devices are desirable over impact printing devices when noise reduction and increased speed of printing are desired.
One typical process for non-impact printing, referred to as ion projection printing, is shown in U.S. Pat. No. 4,088,891 (issued May 9, 1978, in the name of Smith et al). A mask is interposed between an ion generating corona wire and a receiver having a charge receptor surface. An electrode array, associated with the mask, has a control potential selectively applied thereto to set up an electric control field between the electrode array and an electrode behind the receiver. The mask and the electrode array thus exhibit a blocking or transmitting effect on the flow of ions depending upon their relative potentials. The ions are thus selectively placed on the charge receptor surface of the receiver to form a latent image charge pattern thereon. Such charge pattern is subsequently developed with charged pigmented marking particles to form a developed image, which may then be transferred and fixed to a final receiver sheet or fixed directly to the charge receptor surface.
A common electrode array for the mask includes rows of offset apertures. The projected ions from one row are imaged on the charge receptor surface, and thereafter projected ions from the other row are imaged on the charge receptor surface. It has been found that with such an arrangement charges from the previous row of imaged ions tend to repel like charges of the subsequent row of imaged ions so that adjacent lines of charge do not overlap smoothly. This results in alternating dark and light lines which degrades the resultant image. In order to overcome the problem associated with offset aperture electrode arrays, U.S. Pat. No. 4,338,614 (issued July 6, 1982 in the name of Pressman et al) incorporates a slotted focus plane between the aperture mask and the receiver. The slotted focus plane counteracts the repulsion of the ions deposited by a subsequent row of apertures due to the ions previously deposited by the previous row of apertures. However, since the slotted focus plane must be accurately located relative to the aperture mask, the construction of the overall ion projection printhead arrangement is markedly complicated.
Another process for providing ion projection flow is shown in U.S. Pats. Nos. 4,463,363 (issued July 17, 1984, in the name of Gundlach et al) and 4,524,371 (issued June 18, 1985, in the name of Sheridan et al). In such processes, ions are uniformly generated along the length of a corona wire and carried by a rapidly moving transport fluid (air) through an exit channel within which a modulation electrode array is located. A low voltage bias on the modulation electrode array selectively interrupts the ion travel through the exit channel so that a resultant ion beam, of sufficient current density for marking purposes, is provided. As with the above described process, the ion beam is thus selectively placed on a charge receptor surface of the receiver to form a latent image charge pattern thereon. Such charge pattern is subsequently developed with charged pigmented marking particles to form a developed image, which may then be transferred and fixed to a final receiver sheet or fixed directly to the charge receptor surface. Since the electrodes are on the wall of the slot, the electric field is perpendicular to the path of the ions and only serves to reduce ion flow (i.e., does not enhance ion flow). Additionally, since the slot is relatively deep, the ions spend a long time in the slot and many ions are attracted to the walls of the slot making the system relatively inefficient.